The present invention relates to a light absorbing device which comprises an at least partly transparent outer material layer, a space through which a gaseous medium is adapted to be circulated and heated by light radiation passing through the outer material layer, a radiation absorbing material layer which is located in connection to said space, and an element which is adapted to divide the space in at least a first subspace, which comprises a first opening, and a second subspace, which comprises a second opening, wherein the gaseous medium is adapted to flow along a path having an extension from the opening in the first subspace to the opening in the second subspace and that said path has an extension such that the gaseous medium only has possibility to be guided from the first subspace to the second subspace via a passage which is located at a lower level in the space than the levels of the first opening and the second opening, and wherein said element has an extension between an upper end abutting an upper edge surface of the space and a lower end which defines a lower level for an upper portion of the first subspace and an upper portion of the second subspace.
With light is meant here not only light visible for the eye but electromagnetic light in general, comprising ultraviolet light and infrared light.
SE 517 373 shows a light absorbing device according to the above. When the radiation absorbing material layer of the light absorbing device is subjected to incident solar radiation, it obtains an increased temperature. The gaseous first medium, which preferably is air, provides a heating when it comes in contact with the warm radiation absorbing material layer in the space. When the air is heated in the space, the air in one of the subspaces obtains a higher temperature than the air in the other subspace. Thus, a thermal unbalance is obtained between the air in the two subspaces and a natural circulation is established through the light absorber. The natural circulation of air is automatically started when the temperature of the air in the light absorber exceeds the temperature of the air located outside the openings of the subspaces and it ceases automatically when the air in the light absorber has dropped to the same or a lower temperature than the air located outside the openings of the subspaces. The air which is located outside the openings of the subspaces may be air which is located inside a building.
Consequently, such a light absorbing device does not need any energy consuming fan for transporting the medium through the space. The operating expenses for the light absorbing device will thus be substantially non-existent. Consequently, the light absorbing device uses a gaseous medium, which is advantageously air. Thus the light absorbing device does not need any conduits which usually are required for transporting a liquid medium. The risk for leakage resulting in water damages is thus eliminated. The light absorbing device may be given a simple construction and be manufactured to a low cost.
U.S. Pat. No. 4,353,357, U.S. Pat. No. 4,144,871 and U.S. Pat. No. 4,099,513 show all examples of light absorbing devices which comprise an internal box-liked space adapted to be through flown by air heated by incident solar radiation. The air is here guided along a more or less labyrinth-shaped path between an inlet opening and an outlet opening. The object of the labyrinth-shaped path is to give the air a low flow velocity and possibility to come in optimal contact with the radiation absorbing material layer inside the space. Thus, the air may be heated to a high temperature before it is guided out through the outlet opening. However, the use of a labyrinth-shaped path results in the drawback that the air obtains an increased flow resistance. In order to force the air through the flow path, energy consuming fans seem to be needed.